Add support for WaveShaperNode.oversample

Source/modules/webaudio/WaveShaperDSPKernel.cpp

Index: Source/modules/webaudio/WaveShaperDSPKernel.cpp
diff --git a/Source/modules/webaudio/WaveShaperDSPKernel.cpp b/Source/modules/webaudio/WaveShaperDSPKernel.cpp
index 85cdd6a6e608900a18c80102a77a23d00956a298..5544a91acbbcbdcac3469a3d8721a3e0eb1cf1d2 100644
--- a/Source/modules/webaudio/WaveShaperDSPKernel.cpp
+++ b/Source/modules/webaudio/WaveShaperDSPKernel.cpp
@@ -31,12 +31,53 @@
 #include "modules/webaudio/WaveShaperProcessor.h"
 #include <algorithm>
 
+const unsigned RenderingQuantum = 128;
+
 using namespace std;
 
 namespace WebCore {
 
+WaveShaperDSPKernel::WaveShaperDSPKernel(WaveShaperProcessor* processor)
+    : AudioDSPKernel(processor)
+{
+    if (processor->oversample() != WaveShaperProcessor::OverSampleNone)
+        lazyInitializeOversampling();
+}
+
+void WaveShaperDSPKernel::lazyInitializeOversampling()
+{
+    ASSERT(isMainThread());
+
+    if (!m_tempBuffer) {
+        m_tempBuffer = adoptPtr(new AudioFloatArray(RenderingQuantum * 2));
+        m_tempBuffer2 = adoptPtr(new AudioFloatArray(RenderingQuantum * 4));
+        m_upSampler = adoptPtr(new UpSampler(RenderingQuantum));
+        m_downSampler = adoptPtr(new DownSampler(RenderingQuantum * 2));
+        m_upSampler2 = adoptPtr(new UpSampler(RenderingQuantum * 2));
+        m_downSampler2 = adoptPtr(new DownSampler(RenderingQuantum * 4));
+    }
+}
+
 void WaveShaperDSPKernel::process(const float* source, float* destination, size_t framesToProcess)
 {
+    switch (waveShaperProcessor()->oversample()) {
+    case WaveShaperProcessor::OverSampleNone:
+        processCurve(source, destination, framesToProcess);
+        break;
+    case WaveShaperProcessor::OverSample2x:
+        processCurve2x(source, destination, framesToProcess);
+        break;
+    case WaveShaperProcessor::OverSample4x:
+        processCurve4x(source, destination, framesToProcess);
+        break;
+
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+void WaveShaperDSPKernel::processCurve(const float* source, float* destination, size_t framesToProcess)
+{
     ASSERT(source && destination && waveShaperProcessor());
 
     Float32Array* curve = waveShaperProcessor()->curve();
@@ -60,17 +101,106 @@ void WaveShaperDSPKernel::process(const float* source, float* destination, size_
     for (unsigned i = 0; i < framesToProcess; ++i) {
         const float input = source[i];
 
-        // Calculate an index based on input -1 -> +1 with 0 being at the center of the curve data.
-        int index = (curveLength * (input + 1)) / 2;
+        // Calculate a virtual index based on input -1 -> +1 with 0 being at the center of the curve data.
+        // Then linearly interpolate between the two points in the curve.
+        double virtualIndex = 0.5 * (input + 1) * curveLength;
+        int index1 = static_cast<int>(virtualIndex);
+        int index2 = index1 + 1;
+        double interpolationFactor = virtualIndex - index1;
 
         // Clip index to the input range of the curve.
         // This takes care of input outside of nominal range -1 -> +1
-        index = max(index, 0);
-        index = min(index, curveLength - 1);
-        destination[i] = curveData[index];
+        index1 = max(index1, 0);
+        index1 = min(index1, curveLength - 1);
+        index2 = max(index2, 0);
+        index2 = min(index2, curveLength - 1);
+
+        double value1 = curveData[index1];
+        double value2 = curveData[index2];
+
+        double output = (1.0 - interpolationFactor) * value1 + interpolationFactor * value2;
+        destination[i] = output;
     }
 }
 
+void WaveShaperDSPKernel::processCurve2x(const float* source, float* destination, size_t framesToProcess)
+{
+    bool isSafe = framesToProcess == RenderingQuantum;
+    ASSERT(isSafe);
+    if (!isSafe)
+        return;
+
+    float* tempP = m_tempBuffer->data();
+
+    m_upSampler->process(source, tempP, framesToProcess);
+
+    // Process at 2x up-sampled rate.
+    processCurve(tempP, tempP, framesToProcess * 2);
+
+    m_downSampler->process(tempP, destination, framesToProcess * 2);
+}
+
+void WaveShaperDSPKernel::processCurve4x(const float* source, float* destination, size_t framesToProcess)
+{
+    bool isSafe = framesToProcess == RenderingQuantum;
+    ASSERT(isSafe);
+    if (!isSafe)
+        return;
+
+    float* tempP = m_tempBuffer->data();
+    float* tempP2 = m_tempBuffer2->data();
+
+    m_upSampler->process(source, tempP, framesToProcess);
+    m_upSampler2->process(tempP, tempP2, framesToProcess * 2);
+
+    // Process at 4x up-sampled rate.
+    processCurve(tempP2, tempP2, framesToProcess * 4);
+
+    m_downSampler2->process(tempP2, tempP, framesToProcess * 4);
+    m_downSampler->process(tempP, destination, framesToProcess * 2);
+}
+
+void WaveShaperDSPKernel::reset()
+{
+    if (m_upSampler) {
+        m_upSampler->reset();
+        m_downSampler->reset();
+        m_upSampler2->reset();
+        m_downSampler2->reset();
+    }
+}
+
+double WaveShaperDSPKernel::latencyTime() const
+{
+    size_t latencyFrames = 0;
+    WaveShaperDSPKernel* kernel = const_cast<WaveShaperDSPKernel*>(this);
+
+    switch (kernel->waveShaperProcessor()->oversample()) {
+    case WaveShaperProcessor::OverSampleNone:
+        break;
+    case WaveShaperProcessor::OverSample2x:
+        latencyFrames += m_upSampler->latencyFrames();
+        latencyFrames += m_downSampler->latencyFrames();
+        break;
+    case WaveShaperProcessor::OverSample4x:
+        {
+            // Account for first stage upsampling.
+            latencyFrames += m_upSampler->latencyFrames();
+            latencyFrames += m_downSampler->latencyFrames();
+
+            // Account for second stage upsampling.
+            // and divide by 2 to get back down to the regular sample-rate.
+            size_t latencyFrames2 = (m_upSampler2->latencyFrames() + m_downSampler2->latencyFrames()) / 2;
+            latencyFrames += latencyFrames2;
+            break;
+        }
+    default:
+        ASSERT_NOT_REACHED();
+    }
+
+    return static_cast<double>(latencyFrames) / sampleRate();
+}
+
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)